Preservation of rubber



Patented Apr. 9, 1940 1 UNlTED STAT PATENT OFFICE ley, Manchester, England, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No sawi g. Application October 14, 1936, Se-

rial'No. 105,620., In Great Britain October 15,

2 Olaims'; (o1. zed-soc) This invention relates to the preservation of rubber and particularly to the treatment of rubber with compounds which will retardIthe deterioration normally due to the action of lighhheat 5 and oxygen and flexing.

It is well known to those accustomed to handling rubber articles that the rubber perishes withv the passage of time. It is also known to those skilled in the manufacture of rubber. articles that l i 110 rubber can undergo warious types of mechanical failure, such, for instance, as the cracking, which follows repeated flexing .It is known that the perishing of rubber is due largely to oxidation, but the causes of the varivous types of mechanical failure such as flexcracking are less known but it is probable that oxidation is one of them. The preservation of rubber against perishing has long been a go'alfor rubber technologists, and more recently efforts 3 have also been directed towardspreserving the rubber against the various kinds of mechanical failure. The step taken tojeffect this preserva tion is that of incorporating in'the rubber a small-- v wa' new compound, maybe made by exhaustive Y methylation of proportion of a' suita ble preserving agent. The preserving agents are usually spoken of as antioxidants, for reasons which can be seen from the i 'i: colourless crystals m. p. 5456 and boils about foregoing.

An object of the present invention is to provide compounds for retarding the deterioration and flex-cracking of rubber. A still further object is to provide rubber which is more resistant against deterioration due to the action of light, heat and oxygen and flexing. Further objects are to provide new compositions of matter and to-advance the art. Still further objects will appear hereinafter. I The above and other objects are accomplished by the following invention which comprises incorporating with rubber before or after Vulcan-- isation thereof certain tertiary amines..

The compounds which are to be added to rubbar in accordance with our invention constitute a class having the general type formula MFG have been mentioned as preservatives for rubber.

The compounds .of our invention are however better preservatives as canbe seen from the testdata' given hereinafter. t i

- Some of the members of this new class which have been found to be particularly effectiveare as follows:

4-Methoxy- 4-methyl-N-methyldiphenylamine 3-Methoxy-N-methyldiphenylamine, 3'-methoxy-3-methyl-N-methyldiphenylamine, ll-methoxy-4' n'- butyl a N methyldiphenylamine; 2-

i-propoxyi-methyl-N-methyldiphenylamine, 4-

iso propoxy -4-methyl -N- iso propyldiphenyl amine, 4-propoxyfN-propyldiphenylamine, 4 -isopropoxy-N-iso-propyldiphenylamine, and .4-hy- 'droxy-4'-methyl N-methyldiphenylamine;

4-MethoXy-4-methyl-N-methyldiphenylamine,

, 4-hydroxy-4'-methyldiphenylamine with dimethyl sulfate: it forms-almost at 15 mm. 4-iso-Propoxy-N-iso-pr.opyldiphenylamine, a new compound maybe made by alkylating p-hydroxydiphenylamine with excess isopropyl bromide. 4-Methoxy- -n-butyl-N- methyldiphenylamine, a new compound, may be made by methylating 4-methoxy-4-n-butyldi- 'phenylamine with dimethylsulfate: it boils at ISO- at i mm. 4-n-Butoxy-4'-methyl-N- methyldiphenylamine, a new compound, may be made by alkylating 4-hydroxy-4'-methyl-N- methyldiphenylamine with butyl iodide: it melts methoxy-f i':n-butyl-N-methyldiphenylamine, 4- methoxy- 4==-tert.butyl N- methyldiphenylamine,

at 57-66 in the crude state. 4-Hydroxy-4'- methyl-N-methyldiphenylamine may be. made by demethylating 4-methoxy-4-methyl-N-methy1- diphenylamine with hydriodic acid: recrystallised from a mixture of petroleum ether and benzene it 1 formswhite flaky crystals m. p. 75-79". Other In orderto more fully illustrate our invention,-' and the preferred modes of carrying the same into effect and the advantageous results to be obtained thereby, the following example is given.

Example Antioxidant tests were carried out with vulcanisates from the following rubber mixes, mixes F and G being given for purposes of comparison.

A B C D E F Smoked sheet rubber 100 100 100 100 "100 40 40 40 40 40 5 5 5 5 5 4 4 4 4 4 ur 3.25 3.25 3.25 3.25 3.25 Diphenylguanldme 1 1 1 1 1 l 4 methoxy 4' methyl N methyl-diphenylamine. 1 4 methoxy 4 r n butyl N-methyl-diphenylamine. l 4-11 -butoxy- 4- methyl I N-methyl-dlphenylamme. 1

4 hydroxy 4 methyl N methyl-diphenylamme. l. l N-methyldiphenylamine. 1 N-benzyl-N-methylamlma 1 The mixes were vulcanised by heating for 1 hour at 141 C. and samplesfiof the vuloanisates subjected to artificial ageing by'heating at 70 C. in oxygen at 300 1b./sq. infer a period of 4days.

.4 The degree of ageing was then determined by measuring the tensile strengths of the' samples, the following results'be'ing obtained.

Tensile strength in 'samples of the vulcanisates' were also submitted to accelerated flex-cracking tests on the Du Pont' machine (Rubber AgeyNew York, 1930,

26, 542). The resistance of vulcanis'ates, A, B, C and D to flex-cracking was greater-than that of E or F. g a 5 It will be evident from the above example that a large number ofcompounds are adapted for use to come within the scope of the invention. We have shown the hydroxy and alkoxy-N-alkylphenylamines to be effective and also that such compounds containing alkyl substituents in the aryl rings are efiective. The alkyl groups of the 6 alkoxy; N- or .C-alkyl substituents are not limited as to size or nature ofthe chain, we find that the best effects are generally obtained with compounds in which the alkyl groups contain not more than 5 carbon atoms. 10

The antioxidants may be incorporated into the rubberby any well known means such as millin them into thexmixupon the rolls of an ordinary -mill. Moreover; they may be employed in various rubber compounds and in conjunction with other 15 lmown antioxidants such as N:N-diphenyl-pphenylenediamine and phenylnaphthylamines. Also the proportion'of antioxidant may be varied withinwide limits although under normal circumstances about 1% of antioxidant based on 20 the rubber content of the mix-*has been found adequate. These'materials are also efiective in the preservation of other rubber-like materials such as gutta-percha, balata and synth'etic rubbery materials. 125

While we have disolosed'the preferred embodi 'ments "of our'inventionfand the preferred modes of carrying the same into effect, it will" be obvious to those skilled in the art that many variants and modifications" may be made therein without-def parting from thespirit 'of'our' invention. Accordingly our invention is to-be limited solely by the appended claims construedas-broadly as is permissiblein view of the prior art.

We claim: 1. The process for the manufacture of vulcanized rubber' having improved resistance to deterioration and flex-cracking which comprises incorporating in the rubber 4.-methoxy-4- methyl}N-methyldiphenylamine. 2. Rubber having incorporated therein 4- methoxy-4-methyl-Nemethyldiphenylamine.

'1 WILLIAM.-BAIRD. "jRICI-IARDTRANK GOLDS IEIN. 'MALDWYN JONES. "EDWIN'MARSHALL MEADE. 

